As porous materials, zeolites and silica gel have hitherto been known. Zeolites made of aluminosilicates have been practically applied as adsorbents and ion exchange materials, and further, as catalysts. Zeolites are crystalline, have uniform pore sizes, and have excellent properties; however, the pore sizes thereof are as small as about 1 nm or less, and hence zeolites cannot be used as adsorbents or the like for organic compounds larger than the pore sizes. Silica gel has a larger pore size than zeolites; however, the pore size distribution extends widely, which raises a problem of controlling the structure of silica gel.
With such background, there have been developed materials referred to as mesoporous materials in which pores larger than those of zeolites and uniform in pore size are regularly arranged. Mesoporous materials are produced by taking advantage of surfactants, and there have been reported mesoporous materials that are formed of oxides such as SiO2, TiO2 and ZrO2.
As external shapes of mesoporous materials, the following shapes have been reported: an external shape that has no branched portions and is particulate as shown in FIG. 15 (J. Am. Chem. Soc., 126, 2004, 7440-7441 (Non-patent Document 1)), and an external shape that has a branched structure (hereinafter, referred to as “dendritic”) as shown in FIG. 16 (Chem. Commu., 1998, 2461-2462 (Non-patent Document 2)).
Hereinafter, when a mesoporous material is referred to, the whole solid portion of the mesoporous material such as a particulate mesoporous material shown in FIG. 15 and a dendritic mesoporous material shown in FIG. 16 will be particularly referred to as the “framework” of the mesoporous material. The pore shapes of the mesoporous materials have been known to be tubes passing through the framework or to be spheres confined within the framework.
As described above, active studies have been developed on mesoporous materials, but as main structures of mesoporous materials, there have been known only those described in Non-patent documents 1 and 2. Thus, mesoporous materials having new structure that are to be used for functional devices such as biosensors have been strongly demanded.